On Wed, Apr 2, 2025 at 08:29 PM, VA2OJD wrote:
Is there a single spot, somewhere on this forum, where it lists key measurements to check when troubleshooting?
Have you looked at this forum's wiki?? There is a topic specifically for the BS170s.? It has some helpful diagnostic guidance.? And you can search messages in this forum for BS170 and find a good number of entries, with different people being guided in their diagnostic efforts.
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Since your QMX was working for a good amount of time, a good possibility is that you fried your BS170s - most likely just them and not the driver and Q507.? This can occur, especially if you are running FT8 at more than 12.0V (for a 12V build) or 9.0V (for a 9V build).? Or if your QMX puts out more than 5W on a band at the correct voltage.? And especially if you combine over-voltage with some higher SWR on your antenna (probably more than 2:1), which can happen intermittently on wire antennas if the wind is blowing.? Doing any of the above over an extended time has risk of gradually beating your BS170s into failure.? That's why Hans has in big red print in his manuals to a) not run above 12V and b) not run above 5W.? And this is especially true with constant carrier modes like FT8, which add heat in the finals to the mix.? CW is more forgiving, because it is lower duty cycle.? At 5W the BS170s are pretty much up to their rated max, so going above any of the parameters puts more stress on them.? [This is true of their use in (tr)uSDX and other QRP radios, too.]
Stan KC7XE
